When a faucet's valve core leaks while opening, follow these steps: First, shut off the water supply using the shut-off valves under the sink or at the main line. Next, disassemble the faucet by unscrewing the handle and removing the escutcheon plate. Use a wrench to loosen the stem and remove the valve core. Inspect the stem, seat, and O-rings for wear or damage. Clean the seat with a seat wrench or file to remove debris. Replace the valve core if it's damaged, ensuring it fits snugly. Apply lubricant to the stem and reassemble the faucet, testing for leaks. If the leak persists, consider professional repair or replacement.

Valve core leaks occur due to wear, mineral buildup, or misalignment between the stem and seat. According to the U.S. Environmental Protection Agency (EPA), leaks account for 10% of household water waste, with faulty valves contributing significantly. A 2021 study by the American Water Works Association found that 20-30% of faucet leaks stem from valve core issues, often caused by hard water minerals depositing on the seat, reducing seal integrity. Over time, repeated temperature and pressure fluctuations weaken the valve stem, leading to cracks or corrosion. DIY repair is cost-effective, with replacement parts averaging $10-$30, compared to $100-$300 for professional service. Regular maintenance, such as annual seat cleaning and lubrication, can prevent 70% of valve core failures, extending faucet lifespan by up to 10 years. Neglecting repairs can result in water damage, higher utility bills, and potential property damage, emphasizing the importance of timely intervention.